The present invention relates, in general, to an injection unit of an injection molding machine, and more particularly to an injection device for use in such an injection unit.
An injection unit of a type involved here typically includes an injection device which is configured as plunger/screw and operated in a housing for axial as well as rotating movements and which is provided with a backflow prevention assembly. The injection device is provided for plastication during transport of the plastic granulate and acts as plunger, when the plastic melt is pressed through a nozzle into an injection mold. Additives such a colorants, foaming agents, lubricants, or the like, are normally admixed into the plastic granulate before plastication by the screw is carried out.
It is also known to provide conventional plunger-type screw injection molding units with separate metering and mixing devices for mixing and metering the plastic melt as well as additives. These systems suffer, however, major problems as far as a permanent sealing of the shaft and plunger passageways are concerned because jointed areas that move relative to one another must be sealed to prevent against escape of plastic melt.
It would therefore be desirable and advantageous to provide an improved injection unit of an injection molding machine with an injection device, which obviates prior art shortcomings and which is so configured to include a metering and mixing device, without need for sealing moving parts against the outside to prevent escape of melt, while yet being simple in structure and of compact size.